Denitration apparatus



July 24, 9 R. s. EDGETT ETAL DENITRATION APPARATUS 3 Sheets-Sheet 1 Filed Nov. 10, 1954 INVENTOR 190/VALD a 06677 gm/5 a 0450 KWJJMM PIIIIIIIIIL HlJl Illlll lU FIG. I.

ATTO R N EY July 24, 1956 R. s. EDGETT ET AL 2,755,853

DENITRATION APPARATUS Filed Nov. 10, 1954 3 Sheets-Sheet 2 FIG. 3.

July 24, 1956 R. s. EDGETT ET AL DENITRATION APPARATUS 3 Sheets-Sheet 3 Filed Nov. 10, 1954 INVENTOR RON/M0 5 506577 Ans/+15 a OASOIV ATTORNEY DENITRATION APPARATUS Ronald S. Edgett, Pittsburgh, and Arne 0. Olson, Indiana Township, Pa, assignors to the United States of America as represented by the United States Atomic Energy Commission Application November 10, 1954, Serial No. 468,170

9 Claims. (Cl. 15925) This invention relates to a new and improved method and apparatus suitable for converting a liquid slurry, solution or fused solid, into a flowable powder and for handling such power by remotely controlled means. For purpose of illustration the invention is described in relation to its use in the conversion of a fused uranyl nitrate hydrate salt into a uranium trioxide powder although it will be apparent that it is not limited in any way solely to use with these or any other specific materials. The problems presented in the treatment of these particular materials, however, place heavy demands upon the processing apparatus and thus serve as an admirable illustration of the utility of the present invention. For example the need for application of heat in an efficient manner, the fact that a radioactive material is being processed, the fact that corrosive and toxic gases are evolved and the fact that the material in passing from the slurry to the powder states goes through a doughy, putty-like stage, all serve to illustrate the problems existing in the art to which the invention is applicable.

One object of the invention, therefore, is to provide a new and improved concentrating apparatus for efficiently converting a liquefied solid into a powder and for moving the powder without escape of dust to a storage point.

A second object is to provide an improved concentrating apparatus in which caking of material upon an agitator and upon a heating surface is minimized.

A third object is to provide a concentrating apparatus in which leakage of vapors into the surrounding atmosphere is minimized.

A further object is to provide a concentrating apparatus in which boil-over of materials therefrom is minimized.

Other objects and advantages will be apparent when the following description of the invention is considered in conjunction with the drawings in which- Figure 1 is an elevation view showing the preferred arrangement of apparatus with portions illustrated diagrammatically;

Figure 2 is a plan view showing the cover of the concentrating kettle with a portion broken away to show the agitator;

Figure 3 is a view of the agitator and drive shaft;

Figure 4 is a sectional view of a shaft seal; and

Figure 5 is a view of the gulper tube mounting with the agitator drive shaft shown diagrammatically.

in the concentration of uranyl nitrate hydrate salt, taken as an example, various difficulties with conventional concentration apparatus have been experienced. For example, evolved gases such as nitrogen dioxide may leak into the atmosphere, manual unloading of the kettle may permit uranium trioxide dust to escape into the atmosphere, a pufiing action taking place in the kettle near the end of the reaction may cause a belching outwardly of some uranium oxide dust and during the concentration process boil-over of the hot charge may also occur.

As shown in Figure 1, one embodiment of our invention employs a design of apparatus suitable for avoiding or minimizing these difficulties and is shown generally as an 2,755,853 Patented July 24, 1956 assembly view. Upon supporting columns 10 a conventional furnace 11 having a gas inlet means 12 and an exhaust gas outlet means 13, is mounted. The gas inlet means is connected to a series of radiant burners including the usual fiowmixers, air valves, gauges, controls and the like not shown herein. For purposes of disclosure to those skilled in the art, it will be apparent that this controlled source of heat within furnace 11 is adapted to be applied to the external surface of a kettle preferably formed of type 347 stainless steel. This kettle is provided with a removable cover 21 and is suitably mounted in stationary position upon the supporting columns.

A platform 22 mounted above the kettle provides a support for a gear reducer 23 adapted to drive the downwardly extending hollow agitator shaft 24. By means of motor 25 and suitable drive means 26, the shaft 24 may be driven at any desired lower speed and through its connecting hub 27 may cause the agitator 28 within the kettle to move at the desired speed.

Through an aperture in the gear reducer, a hollow tube, hereafter called the gulper tube is adapted to pass and to extend downwardly within the hollow agitator shaft. At its non-rotatable upper end the gulper tube terminates in the vacuum connection section 31. At its lower rotatable end 4% the tube in extended position reaches to within a small fraction of an inch of the bottom of kettle 20, the entire tube, however, being supported from a movable plate 32. Plate 32 is provided with hollow sleeves 33 adapted to move along stationary guide rods 34 and has a web section 35 to which is attached a control rod 36 actuated by a suitable servomotor means, indicated by the hydraulic cylinder 3'7.

As best shown in Figure 5, movable support plate 32 by means of brackets 41 supports a suitable thrust bearing preferably formed of stainless steel and capable of operating under heavy loads at relatively high temperatures. This bearing includes a ball race section 42 secured to the lower rotatable section of the gulper tube and a ball race section 43 securely mounted against rotation and motmted in bracket 41. Between the non-rotatable upper portion 31 of the gulper tube and the rotatable lower portion 40 thereof is a small but important air gap 45 the function of which will later be described. This gap may be as small as & inch and still fulfill its function. Rotatable portion 40 of the gulper tube is provided on its lower exterior surface with a series of vertically disposed keys 46 adapted to fit into matching keyways 47 on the interior of the rotatable hollow agitator shaft 24 (Fig. 3). Portion 40 of the tube is open at its lower end and also is provided with a series of small apertures 48 in its wall adjacent the lower end of the tube. Adjacent the point on the tube at which its enters into the aperture within gear reduction box 23 (shown schematically in Fig. 5) a dust shield or cover 49 may be attached to the tube for rotation therewith and for preventing foreign materials from entering the gear box.

Referring now to Figure 4 a suitable sealing means for confining the vapors and contents of the kettle is shown. As noted, the rotatable portions 40 of the gulper tube splined to the rotatable agitator shaft 24 enters the cover 21 of the kettle through an aperture in the cover. Mounted upon the cover is a labyrinth stationary seal to which a sealing liquid may be supplied by conduit 50 and from which the liquid may drain after reaching the prescribed level through conduit 51. A conventional two piece ring clamp 52 mounted upon the upper portion of the labyrinth seal can be adjusted to bear in light frictional contact with the outer surface of the rotatable agitator shaft. As a result, vapors generated within the kettle and not adequately removed by the vacuum connections later to be described are confined within the thus described seal and cannot be vented to the atmosphere. Furthermore, any

puffing action taking place in the kettle will not be able to expell solids along the rotatable shaft since the seal will serve to contain such materials. As indicated the splined tube 40 and shaft 24 are mated with a close fit and virtually no vapors are able to pass outwardly therefrom into the gear reduction box.

As shown in Figure 2 the kettle cover 21 is provided with numerous apertures to which operating and control devices of conventional nature may be attached. For example, a large access opening 60, normally closed with a suitable removable cover, is provided. A large vacuum outlet 61 adapted to be connected to a vacuum system, not shown, is employed to remove vapors such for example as H2O, NO and N02 during the concentration of the material in the kettle. The application of vacuum during the processing stages constantly removes the evolved vapors and prevents the sudden building up of pressures which otherwise could cause a boil-over. In addition an inlet aperture 62 is adapted to be connected to the source of flowable material to be concentrated, apertures 63 and 64 provided with conventional ball joints may be used for insertion of means to clean out encrustations within the kettle; and thermometer wells 65 and 66 may be suitably disposed at points where no interference is encountered with the moving agitator. Moreover, a vacuum breaking connection 67 and a sight glass connection 68 customarily are used while the aperture 69 (see Fig. 4) provides for the entrance of the rotatable shaft and gulper tube. On its inner surface intermediate the openings provided for these various control means, the cover preferably is provided with heat insulation impervious to the materials under treatment in the kettle.

As shown in Fig. 3 the agitator 28 is securely aflixed to shaft 24 by means of a hub 27. While many varied forms of agitator may be employed without departing from the invention, we have found in processing a material such as that exemplified that means should be provided for rotation of the agitator in either direction. Accordingly, we prefer to employ stirrer blades 70 and 71 suspended from the top beam 28 of the agitator and reaching to within a small fraction of an inch of the inner surface of the kettle 20. Preferably these blades have a substantially triangular cross section with the base thereof adjacent the kettle surface with the result that movement of the blades elfects a lifting action upon material adjacent the kettle surface. Projecting from opposed surfaces of the blades is a series of detachable fins, 72 and 73 which upon rotation of the agitator in one direction tends to move material toward the circumference of the kettle and upon rotation in the opposite direction tends to move the material toward the center of the kettle and adjacent the location of the gulper tube. The fins 72 and 73 may be detached when necessary in accordance with the nature of the material being processed. As noted in Figure 3, various bracing means are employed including a thin tie plate 74 between the inner ends of the blades and diagonal braces 75 and 76 adjacent the outer ends of the blades. As diagrammatically shown in this figure, a thermometer well 77 and a wash inlet and sparger conduit 78 are mounted upon the kettle cover in locations which do not interfere with the movement of the agitator assembly.

Having thus described the improved apparatus, a preferred mode of operation when treating the material used as an example is as follows. Assuming that a batch operation is to be employed, a quantity of the liquefied material to be concentrated is introduced into the kettle through inlet aperture 62, the lower end 40 of the gulper tube having been first lifted by means of hydraulic cylinder 37 into its uppermost position. At this time suitable vacuum connections are applied to the upper portion 31 of the gulper tube and to the vacuum outlet 61 of the kettle and upon application of the vacuum, the major portion of any vapors evolved from the heating of the uranyl nitrate hydrate charge are carried out through the outlet 61. However, some process gases such as nitric acid vapor, water vapor and nitrogen oxides tend to pass out through the hollow gulper tube and by means of the air gap 45 between the rotatable and non-rotatable portions of that tube, a regulated amount of diluting air can be mixed with those gases. The movement of such air and gases passing through the tube section 31 keeps the entire gulper tube flushed clean of process gases and assists in the efliciency of the concentration taking place in the kettle. At the same time the entrainment of the process gases with the air prevents such gases from remaining in contact with the equipment and causing corrosive action.

At the same time, heat is being applied to the outer surface of the kettle and the agitator is being driven preferably in a counter clockwise direction as viewed in Figure 2. Usually the material entering the kettle is about 225 F. and may be thereafter heated to the range of 400 F. or more. During the early heating the water of crystallization is boiled off and initial turbidity of the charge occurs at about 312 F. A typical operation would include concentration steps of the following sequence: charging the material to the kettle at about 225 F. with heating being applied simultaneously; after about one half hour the material reaching a boiling stage; after about four hours the material attaining a temperature of about 400 F.; after about five and one quarter hours the material changing to a thin grainy dough; after about six hours the material changing to a slick dough; then the material passing through the stages of stiff dough and chunks of dough and finally the material reaching the stage of a fine powder about seven and one half hours after entering the kettle.

After reaching the fine powder stage the heating can be discontinued and if discharge of the hot powder is desired immediately the gulper tube can be moved to the bottom of the kettle and sufficient vacuum applied to the portion 31 of the tube to start tthe unloading operation. At this time the vacuum to outlet 61 can be interrupted and the direction of rotation of the agitator shaft reversed. Moving the agitator clockwise as seen in Figure 2 assists the flow of the powder toward the lower central portion of the kettle and banks it around the lower end 40 of the gulper tube where it can be drawn outwardly by the suction means attached to portion 31 of the tube. The adjustable air gap 45 is used during this step in the processing to bleed a regulated amount of air into the tube. The air in this case is mixed with the dust-like product to eliminate any possibility that the material will clog the tube. Upon completion of the evacuation of the powder, the gulper tube can be raised and the equipment is ready for the next batch. During the described removal of the final product from the kettle, the dust, which in this case is radioactive in character, is kept confined within the equipment and does not escape into the atmosphere. The cover is kept on the kettle at all times during the unloading and the operator of the equipment is not required to be in close proximity to the material being handled.

Having thus described our invention it will be apparent that modifications will be readily suggested to those skilled in the art, which modifications would come within the scope and purview of the invention. Accordingly, our invention is not to be limited except insofar as set forth in the following claims.

What is claimed is:

l. Concentrating evaporation apparatus including a kettle, a cover for the kettle, means for heating the kettle, means for withdrawing evolved vapors from the heated kettle, a hollow rotatable agitator shaft extending through said cover into the kettle and a hollow product removal means mounted within said shaft and selectively movable along the axis thereof, whereby the contents of the kettle may be withdrawn without removal of said cover.

w 2. Apparatus as defined in claim 1, wherein said product removal means includes a non-rotatable portion outside the kettle and a rotatable portion inside said kettle.

3. Apparatus as defined in claim 2 wherein said rotatable portion is driven by the agitator shaft.

4. Concentrating evaporator apparatus including a kettle, a cover for the kettle, means for heating the kettle, means for withdrawing evolved gases from the heated kettle, a hollow rotatable agitator shaft extending through said cover into the kettle, a hollow product removal means mounted within said shaft and selectively movable along the axis thereof, said removal means comprising a non-rotatable portion outside the kettle and a rotatable portion inside the kettle with said portions being separated by an air gap, whereby upon application of a vacuum to said nonrotatable portion any vapors issuing from said rotatable portion may be entrained with air flowing through said gap and removed to a point of disposal.

5. Apparatus as defined in claim 4 wherein said product removal means is mounted for reciprocal movement with respect to said shaft while retaining a given setting of said air gap.

6. Apparatus of the class described comprising an evaporator adapted to prevent accidental release of its contents into the atmosphere and including, a kettle, means for heating the kettle, an apertured cover for said kettle, a hollow rotatable agitator shaft extending through an aperture in said cover, a labyrinth seal attached to said cover adjacent the aperture and surround- 6 ing said shaft, means attached to said cover for withdrawing evolved vapors and minimizing boil-over pressures, and a hollow product removal means mounted within said shaft and selectively movable along the axis thereof.

7. Apparatus as defined in claim 6 wherein said prod uct removal means includes a rotatable portion inside the kettle and a non-rotatable portion outside the kettle.

8. Apparatus as defined in claim 7 wherein said rotatable portion is driven by the agitator shaft.

9. Apparatus of the class described comprising an evaporator adapted to prevent accidental release of its contents into the atmosphere and including a kettle, an apertured cover for the kettle, means for heating the kettle, a hollow rotatable agitator shaft extending through said cover into the kettle, a hollow product removal means mounted within said shaft and selectively movable along the axis thereof, said removal means comprising a non-rotatable portion outside the kettle and a rotatable portion inside the kettle with said portions being separated by an air gap through which air may be drawn to sweep from said removal means any vapors escaping therethrough, a labyrinth seal attached to said cover adjacent the aperture and surrounding said shaft and means attached to said cover for withdrawing evolved vapors from the heated kettle and minimizing the occurrence of boil-over pressures therein.

No references cited. 

1. CONCENTRATING EVAPORATION APPARATUS INCLUDING A KETTLE, A COVER FOR THE KETTLE, MEANS FOR HEATING THE KETTLE, MEANS FOR WITHDRAWING EVOLVED VAPORS FROM THE HEATED KETTLE, A HOLLOW ROTATABLE AGITATOR SHAFT EXTENDING THROUGH SAID COVER INTO THE KETTLE AND A HOLLOW PRODUCT REMOVAL MEANS MOUNTED WITHIN SAID SHAFT AND SELECTIVELY MOVABLE ALONG THE AXIS THEREOF, WHEREBY THE CONTENTS OF THE KETTLE MAY BE WITHDRAWN WITHOUT REMOVAL OF SAID COVER. 